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Horizontal Gene Transfer in the Human GI Tract
Human Gastrointestinal Tract There are many different species of normal microbiota that are regularly found in the human gastrointestinal tract. Most of this bacteria is used to digest food and other particles to create energy for the body, also to create a way for waste to leave the body. There are 1014 individual bacterial cells and many different biofilms are found in the gastrointestinal tract. Of all these different species, there are some strains that can create deadly infections in the human body. Most of these infections can be treated with antibiotics, unless they have acquired antibiotic resistance genes. Some ways these microbiota could acquire antibiotic resistance is through mutations or horizontal gene transfer. Horizontal Gene Transfer There are three different types of horizontal gene transfer: conjugation, transformation and transduction. Conjugation is the most studied when pertaining to the human gastrointestinal tract. Conjugation is the process fo transferring DNA using many different mechanisms: * Cell to cell contact * Mating pair formation * Conjugative pilus Antibiotic resistance can be transferred between microbiota in the human gastrointestinal tract using any three of htese mechanisms. Non-conjugative plasmids (non self-transmissible) can be transferred using conjugative machinery, One thing that complicates the plasmid transfer is that other non-plasmid can be transferred using conjugation; basically any gene can be mobilized and transferred using a mobile genetic element such as conjugation. Transformation Antibiotic resistance is also acquired through natural transformation. Natural transformation allows for the uptake of plasmid DNA as well as chromosomal DNA.There are 5 models why bacteria take up DNA from the environment, all bacteria must be induced to competence before being transformed: * Nutrient source * Templates for DNA repair * Increasing genetic diversity * Indirectly selecting for non-growing competent cells * Unintended consequence of type IV cell adhesion Role of HGT in Antibiotic Resistance Biofilms have been shown to be an ideal environment for horizontal gene transfer since they allow for for high bacterial density and can physically protect the bacterial cells. High bacterial density allows for bacterial cells to be in close proximity to each other, creating easy cell to cell adhesion. Many different studies have been conducted to show that HGT has created a way for antibiotic resistance genes to be passed from bacterial genus to bacterial genus. Examples "A study comparing the gut metagenomes from 275 individuals to the sequences deposited in the ARDB showed resistance to 53 antibiotics. The study also found multiple antibiotic resistnace genes on contigss with integrase and transposase, indicating the possibility that these clusters are part of mobile genetic elements." An analysis of a nosocomial outbreak of Enterobacter cloacae revealed there was a conjugal transfer of a specific coin plasmid from E. cloacae to other bacterial members of Enterobacteriaceae in the intestines of a specific patient, which then had spread to other patients. A case study reported the probably transfer of multidrugg resistance plasmid from Kelbsiella pneumonia to Escherschia coli in the gastrointestinal tract of a patient. After treatment with ertapenem, metronidazole, colistinn and vancomycin, there was carbapenem-resistant E. coli strain present in the gastrointestinal tract of this patient.